IOWA
CITY, Iowa - A University of Iowa researcher has received a two-year,
$95,600 contract from the Alaska Department of Fish and Game (ADF&G) to
provide information that may help the state of Alaska better manage its shellfish
industry -- in particular, the weathervane scallops that grace our dinner
tables.

Scott Carpenter, (click on photo for enlargement and further details) associate
research scientist for the UI Center for Global and Regional Environmental
Research (CGRER) and manager of the Paul H. Nelson Stable Isotope Laboratory,
says that fisheries experts will benefit from definitive chemical data --
rather than visual estimates -- of the age and growth rates of scallop populations.

"One goal of this project is to compare the visual shell-aging technique
(similar to counting tree rings), currently in use, with shell ages determined
from oxygen isotope analysis," he says. "Definitive age determinations
are fundamental to the improved management of scallop beds along the Alaskan
coast and around the world."

Volunteer observers on scallop boats will collect shells from some eight
shellfish sites (in the Gulf of Alaska and Bering Sea. The shells will be
shipped to the UI's Paul H. Nelson Stable Isotope Laboratory for analysis
by Carpenter and Curtis Moss, a senior undergraduate research assistant from
Clinton, Iowa majoring in geoscience in the College of Liberal Arts and Sciences.
Small amounts of shell will be milled out (using a modified dental drill)
at approximately one-millimeter intervals across the outer surface of the
shell and analyzed for carbon and oxygen isotope ratios. The collection of
nearly 300 such analyses per shell produces a detailed life history, typically
5-15 years, of each organism. By documenting the annual temperature changes
recorded in the shell chemistry, it is possible to precisely determine the
age of a shell. In addition, these analyses can be used to determine the age
at which scallops reach sexual maturity. By knowing the age and maturation
differences for each site, the ADF&G can avoid over-fishing of these fragile
communities.

Carpenter notes that the study will also include related activities, such
as:
 Genetic testing to assess similarities among the various populations.
 Relocation of living scallops to different sites where growth rates
will be monitored under controlled conditions.
 Comparisons of modern
data with those from fossil scallop shells to estimate ancient seawater temperatures.

In addition to determining the age of shells, he will gather data on the
effects of El Nino on the temperature of waters in the Gulf of Alaska over
the last decade. "These data permit historical monitoring of numerous
locations during a time of several El Nino events, particularly the very large
El Nino of 1997-98," Carpenter says. "This permits a detailed reconstruction
of oceanographic conditions over a wide geographic area over several years.
He adds that this research will be the first documentation of El Nino-related
temperature changes at a water depth of approximately 100 meters for a large
portion of the Gulf of Alaska coastline, an area of critical importance to
the fishing industry of the remote and complicated northeastern Pacific Ocean.